Wood-pulp-grinding plant and the art of operating the same



July 23, 1929. F. GROSSLER ,7

WOOD PULP GRINDING PLANT AND THE ART OF OPERATING THE SAME Filed Feb. 9. 1928 2 Sheets-Sheet 1 V n enter Ffi/HJ/i/CH Gfio'ssz Hi July 23, 1929. F. GROssLER 1,721,863

WQOD PULP GRINDING PLANT AND THE ART OF OPERATING THE SAME Filed Feb. 9, 1928 2 Sheets-Sheet 2 J0 ven to r' r/mwR cw cwdsszm Av-mhne v Patented July 23, 1929. I

UNITED STATES.

FRIEDRICH GRGSSLER, 0F HEBMSDORF (RIESENGEBIRGE), GERMANY, ASSIGNOR TO LINKEHOFMANN-WERKE A. G. ABTEILUNG FULLNERWEBK, OF WARMBRUNN',

SCHLESIEN, GERMANY.

WOOD-PULP-GRINDING PLANT AND THE ART OF OPERATING THE SAME. I

Application filed February 9, 1928, Serial No.

The invention relates to an improvement in wood pulp grinding plants and in the art of operating the same.

In the operation of wood pulpgrinding machines it is an essential requirement that the speed of the pr Jne mover driving the grinding stone be maintained absolutely constant. Numerous disadvantages result from a failure to comply with this requirement, forinstance, the impossibility of producing a high grade product because such variations in the speed of the grinding stone as may be caused by a change in the load, affect the quality of the pulp produced.

The customary manner of regulating the speed of the prime mover coupled with the grinding stone consists in automatically con trolling the energy produced by the prime mover in orderto compensate for changes in the load and to keep the speed invariable. Uusually mechanical regulators serve for this purpose, particularly, when the prime mover is formed by steam engines, combustion engines or the like. Such mechanical regulators are not sufficiently sensitive to respond without delay to changes in the speed of the grinding stone. A delay in the response, however, results in fluctuations of the speed and experience has shown that these fluctuations amount at least to.10 pet. in the case of a. grinding plant driven by a prime mover provided with an ordinary centrifugal regulator.

One object of my invention is the provision of a regulating device by means of which the fluctuations of speed may be kept down below the limit of 1 pct. 7

Another object of the invention is the provision of a regulating device which responds immediately and without delay to variations in the velocity or speedof the grinding stone or of the prime mover coupled therewith.

From another aspect, an object of the invention is the provision of a method of main taining the load of the grinding stone constant whereby an invariable speed is insured without requiring a. control of the energy developed by the prime mover at its predetermined normal speed. While the invention may be. applied to any wood pulp grinder, it is particularly adapted for use in such grinders which have a continuously operating feeding mechanism, such as shown 253,168, and in Germany February 14, 1927.

and described in United States Patent No.-

Wood pulp grinders are frequently driven by a hydraulic turbine equipped with a mechanical regulating mechanism which permlts an automatic control of the energy produced at normal speed to compensate for changes in the load. Such a mechanism, however, is expensive and complicated. It is desirable, therefore, to render the same dispensable, so that water turbines may be used in which the energy developed at a certain speed need not be varied. As the invention consists in an electrical regulating mechanism, which maintains the load constant, it creates the possibility of installing in grinding plants hydraulic turbines not equipped with the afore-mentioned automatic mechanical regulating mechanism.

. Further and more specific objects of the invention will appear from. the description hereinafter and the features of novelty will be pointed out in the claims. Two embodiments of the invention are illustrated in the accompanying drawing.

Fig. 1 shows 1n a diagrammatical fashion a grinding plant comprising a water turbine coupled with a grinder of the type shown and described in the Patent No. 1,652,044 which is equipped with an embodiment of the novel regulating mechanism, Fig. 2 shows a similar arrangement.

10 indicates the prime mover which, in

this instance, is formed by a water turbine,

and at 11 the grinding stone of the wood pulp grinder is shown. As the grinder corresponds substantially with thatshown and described in the Patent No. 1,652,014, a detailed description thereof may be dispensed with herein. For sake of clearness it may be mentioned, however, that the feeding shaft filled with logs is indicated at 12. The walls of the shaft 12 are formed by feeding screws 13. The feeding screws are rotated an electromotor 14. I

The diagrammatically illustrated axle 15 of the water turbine, on which the grinding stone is mounted, is equipped with a pulley' l6' driving an electromotor 17 by means ;of a belt 18. While in the illustrated embodiment the motor is of the commutator type with a shunted field winding, any other electromotor may be used, c. g. a commutator motor having field and armature wound in series.

The feeding means of the grinder, such as the threaded spindles 13, are provided with a controlling mechanism to control the speed with which the wood is fed against the grinding stone. In the embodiment shown in Fig. 1 the controlling mechanism comprises an electromotor 14 which is in driving connection with the spindles 13, and a generator 15 supplying the motor 14 with electric energy.

yyregulating the degree of encrgization of the field 16 of the generator 15, the amount of the energy produced and thereby the speed of inotor14 may be varied. The generator 15 is driven by a suitable motor 17, e. g. by a threephase induction motor connected with a suitable source 18 of a three-phase current.

The field 16 is supplied with current from any suitable source, for instance from a small generator 21 coupled with the generator 15. The intensity of the current circulating through the field 16 is regulated in proportion to the strength of the current developed by the generator 17. While this regulation may be efiected by simply supplying the field 16 with the current produced by the generator 17, another more appropriate way is chosen in the illustrated example. Connected with the polesof the generator 17 is an apparatus 24 which contains a variable resistance 25 and means to automatically vary this resistance 25 in proportion tothe current supplied to said means from the generator 17 The resistance 25 is inserted in the circuit of the field 16. As the apparatus 24 is well known and available on the market (in Germany it is manufactured by the firm Brown, Boveri & Cie. and on sale under the name Schnellregler) and as the salne does not form a part of the invention, the description of this construction need not be given herein.

The operationof the embodiment shown in Fig. 1 is as follows:

It may be assumed that, owing to a decrease in load as may be caused by the occur: rence of some softlogs in the wood pile, the speed of the turbine 10 tends to increase. The slightest increase, however, e. g. an increase of less than one pct., results in a substantial increase in strength of the current produce d by the generator 17. As a consequence, the apparatus 24 reduces the resistance 25 so that the energization of the field 16 is intensified. The generator 15 consequently produces a stronger'current than before, thereby speeding up the motor 14. This effect coincides nearly exactly with the increase in velocity of the turbine 10. The increase in velocity, therefore, causes an immediate increase in feedings speed and, thereby, in the load int-- A posed on the grinding stone by the logs so that any further increase in velocity is effectively counteracted.

The embodiment shown in Fig. 2 difl'ers diately reduces the resistance 25.

and connected by means of a belt with a pulley 28 which is diagrammatically shown as coupled with the primary shaft 29 of a hydraulic gear 30. The secondary shaft 31 of this gear is in driving connection with the spindles 13. The ratio of transmission of the gear may be varied by adjustmeiitpf a lever 32 journaled at 33 in the housing of the gear.

While any suitable hydraulic gear may be used which permits a continuousregulation of the transmission ratio within the required limits, a gear is preferred which is on sale on the German market under the name Lauf- Thoma-Getriebe. The adjusting lever 32 is connected with a servo-motor comprising a piston 33 movable in a cylinder 34 filled with oil. Both ends of the cylinder communicate with a second cylinder 35 by means of conduits 36 and 37. A piston valve 38 mounted in the cylinder 35 is provided with a recessed central section 38 the length of which corresponds with the distance between the conduits 36 and 37. The width of the non-recessed ends of the piston 38 corresponds with the width of the conduits 36 and 37. The central part of the cylinder 35 is provided with a portconnected to a pipe 39 supplying oil under pressure from some suitable source. The ends of the cylinder 35 communicate with another oil pipe 40 within which a lower pressure prevails than in the pipe 39. On the end of the piston rod of the piston 33 a double-armed lever 41 is pivoted having its lower arm in pinand slot-connection with the piston rod of the piston'valve 38 The other arm of the lever 41 is also attached by means of pin and slot to an iron core 42 movably supported in a stationary frame 43,

which. is shown as attached to the cylinders 34 and 35. The core 42 is subjected to. the resilient force of a spring 46 and surrounded by When owing to a. decrease in load which may be caused by the occurrence of particularly soft logs, the speed of the axle or shaft 15'tends to increase, the apparatus 24 imme- Consequently, the current circulating through the coil 44 is increased and the core 42 is drawn to the right against the action of a spring 46,

until a new position of equilibrium is reached between the force exerted by the spring 46 and the increased magnetic force. When the valve 38 occupies the position shown in the drawings, the piston 33 cannot move because both conduits 36 and 37 are closed by the pis- 'ton valve 38. When, however, the upper end of the lever 41 is moved to the right by the core 42, the lower end will be swung to the left thereby displacing the valve 38. Consequently, the central recess thereof supplied with oil, under pressure will get into communication with the left end of the cylinder 34 while the right end thereof is brought into communication with the return pipe 40. The pressure exerted on the piston 33 from the left moves the same to the right, which movement displaces the adjusting lever 32, and, coincidentally returns the lower end of the lever 41. The movement will continue until the piston valve 38 has been returned into the position illustrated in the drawings. The displacement of the lever 32 to the right changes the transmission ratio of the gear 30 in such a manner as to raise the speed of the shaft 31 whereby the load imposed upon the grinding stone will be increased; This increase in load counteracts the tendency of the turbine 26 to speed up, whereby the velocity of the turbine and the grindstone is maintained constant.

As the piston 38 does not offer any appreciable resistance to the lever 41, it moves immediately in response to a change in intensity of the current developed by the generator 17.

From the foregoing it is apparent that in a broad aspect, the invention may be viewed as a method 'to develop an electric current in dependence upon the s ed of the prime mover, and to utilize this current for infiu encing the speed with which the wood is fed to the grinding stone. In spite of the absence of any turbine regulator permitting a variation in the energy produced by the water turbine, a constant speed thereof is maintained. Owing to this fact, other machines requiring a uniform speedsuch as an elecfiric generator for illuminatin purposes may e coupled with the water tur ine.

What I claim is r-- 1. In a wood pulp grinding plant, the rpmbination comprising a prime mover, a grinding stone in driving connection therewith,

wood feeding means to press the pulp wood against said stone, a controlling mechanism to control the speed of said feeding means, a generator connected with said prime mover to be driven with a speed proportional to the velocity of said prime mover whereby an electrical current is generated depending in strength upon said velocity, an electric device influenced by said current and operatively connected with said controlling mechanism to cause an acceleration of the feedin speed when said velocity increases where y any change in said velocity is immediately counteracted.

2. In a wood pulp grinding plant, the combination comprising a 'water turbine of the type in which the velocity depends upon the load imposed,a grinding stone in driving connection therewith, wood feeding .means to press the pulp wood against said stone, a controlling mechanism to control the speed of said feeding means, a generator connected with said water turbine to be driven with a speed proportional to the velocity of said water turbine whereby an electrical current is generated depending in strength upon said velocity, and an electric device influenced by said currentand operatively connected with said controlling mechanism to cause an acceleration of the feeding speed when said velocity increases whereby any change in said velocity is immediately counteracted.

J 3. In the art of operating wood pulp grinding plants including a'prime mover, a grinding stone coupled therewith and feeding means to feed wood against said stone, the method of regulating the velocity of the prime mover consisting in generating electric currentin dependence on said velocity and using said current for the exclusive control of the speed of said feeding means whereby an increase in said velocity will cause an immediate increase in said feeding s eed and, correspondingly, an increased 10a imposed upon said prime mover.

In testimony whereof I aflix my signature. 

